The present invention relates to a shutter blade device for use as a shutter of a compact camera or an iris stop, and more specifically relates to a device of the type having a plurality of blades disposed slidably over an aperture to move from the aperture in opposite directions. The blades are superposed successively to cover the aperture.
The conventional compact camera is provided with a shutter device of the type having a pair of blades slidable relative to a lens aperture in opposite directions to one another to effect opening and closing of the aperture. This type of the shutter device is operative to control an opening time interval and an opening diameter by their blades and has relatively small size and light weight suitable for use in the compact camera. However, this type of the shutter device is needed to use a pair of blades of relatively great dimension to cover an aperture having a relatively great diameter effective to reduce F number of lens system in the compact camera. In such case, the pair of blades are stored on opposite sides of the lens aperture so as to open the aperture The greater the dimension of each blade, the more the planar spacing for storing each blade within an outer boundary of the device, thereby causing a drawback that the outer diameter of the device is enlarged.
In view of the above noted drawback of the two-blade type shutter device, there has been proposed another type of the shutter blade device as disclosed, for example, in Japanese Patent Laid-Open Application No. 526/1989. This type of the shutter device is designed such as to facilitate enlargement of a lens aperture diameter to reduce F number without enlarging an outer diameter of the shutter device. Namely, this type of the shutter device is provided with two pairs of blades such that each pair is comprised of an inner blade and an outer blade, and one pair corresponds to one blade of the first-mentioned conventional shutter device. The four blades are overlapped with each other to completely close the lens aperture, and the respective pairs are stored in superposed relation on opposite sides of an annular area around the lens aperture within an outer periphery of the shutter device structure. Stated otherwise, one blade is divided into the inner and outer blade sections to enable compact storage of the two blade sections in the superposed relation.
However, in the shutter device disclosed in Japanese Patent Laid-Open Application No. 526/1989, the four shutter blades are pivotably supported around a common shaft pin on a periphery of the lens aperture. The respective blades are slidably driven by four operating pins. The four operating pins are disposed adjacently to each other so that the respective blades have a complicated shape formed with recesses so as to escape movement passe of the operating pins closely arranged with each other. Therefore, design freedom of shutter blade shape is unduly restricted. Further, the four blades are rotated around the common shaft pin in opposite directions relative to the lens aperture to define an effective opening bordered by the opposed inner edges of the separating blades. However, the shape of the effective opening is distorted from a circle, thereby causing a drawback that exposure amount of the shutter cannot be controlled accurately.